The invention relates to apparatus for pumping fluids and more particularly, to a design for a shaft driven pump for liquids which eliminates the necessity of a seal about the driving shaft where it enters the pump casing.
Pumps are typically either of a shaft or shaftless design. This invention relates to the former. Such pumps typically comprise a motor or some other driving mechanism, a pump casing or chamber housing a rotor or other impeller and a shaft connecting the driving mechanism to the impeller for actuating the same. A mechanical seal is generally provided about the shaft where it penetrates the pump chamber so as to prevent leakage of the fluid being pumped and to otherwise maintain fluid pressure created by the impeller to assure efficient pumping.
There are significant negative aspects associated with such seals. Typically, seals are subject to wear or damage necessitating their replacement as well as possible replacement of the shaft. Also, contact between the seal and the shaft causes frictional drag upon the shaft reducing pump efficiency. Moreover, a sufficiently high initial torque must be provided to overcome standing friction between the seal and the shaft when the latter is initially rotated imposing further constraints on the motor or other drive mechanism selected to drive the impeller.
Various "sealless" pump designs have been proposed to overcome some of these problems. For example, U.S. Pat. No. 4,065,232 describes a vertically oriented shaft driven "sealless" centrifugal type fluid pump. Fluid leaking from the pump chamber rises about the shaft into a sealed adjoining upper chamber where gas is introduced to control the level of the fluid. A conduit is provided to the inlet of the pumping chamber and is used to remove excess fluid from the upper chamber. This system requires a gas source as well as auxiliary equipment controlling the introduction of gas into and monitoring the level of fluid within the upper chamber.
As will be described subsequently in greater detail, applicant's invention involves the use of a second impeller in a sealless pump design to control fluid leakage from a primary pumping chamber along the pump drive shaft. Of relevance to this aspect of my invention is British Pat. No. 1,389,222. That patent describes a vertically oriented shaft driven pump for liquid fuels having a primary pump chamber at the bottom of a pump housing, a secondary pump chamber above the primary pump chamber and a motor housing above the two pumping chambers. A shaft extends from the motor through the secondary chamber and into the primary chamber where it drives a primary pump centrifugal type rotary impeller. The shaft also drives a secondary centrifugal type rotary impeller in the secondary pump chamber which removes liquids leaking into the secondary chamber and draws air from the motor housing to prevent fumes from the pumped fuel from invading the motor. The indicated design does not dispense with seals as a conventional mechanical seal is supplied around the shaft between the primary and secondary pumping chambers. Lastly, a separate outlet must be provided for the removal of fluids (fuel, fumes and air) from the secondary chamber, additionally complicating its design and increasing manufacturing costs.
Also of relevance to the multiple impeller aspect of my invention is a class of fluid pumps represented by U.S. Pat. Nos. 4,088,424 and 4,226,575 used with wet pickup vacuum cleaners and/or rug shampooers. Each patent describes a pump apparatus comprising a plurality of impellers mounted upon and driven by a common shaft for rotation. The impellers operate in two chambers defined by walls of the apparatus housing. A fluid path is provided between the chambers by an opening about the impeller drive shaft. Fluid entering the apparatus and first chamber through an inlet is urged through the opening and into the second chamber where other impellers urge the fluid towards an outlet from that chamber and the apparatus. The function of at least one impeller in the second chamber of each invention is to create a pressurized air barrier preventing the fluid being pumped, a mixture of air, moisture and perhaps other liquids, from travelling to the base of the impeller drive shaft and into contact with the motor or its bearings. The one impeller acts as a blower drawing air from an external source and pumping it under pressure into the fluid being moved by the remaining impellers causing the pumped fluid to continue along a path towards the outlet. The air seal thus formed by the pressurized air is undesirable in certain applications as air is mixed into the fluid being pumped. It is also believed the system would be ineffective against fluids which are entirely or primarily liquid.